1. Field of the Invention
The present invention relates to a communication channel set up method and a communication control device, and more particularly, to a communication channel set up method and a communication control device for reducing interferences between radio communication systems using radio signals of close frequencies.
2. Description of the Related Art
As a method for avoiding interferences between radio communication systems using radio signals of close frequencies, a method for providing the so called guard band between frequency bands used by the respective radio communication systems is known. In this method, there is a need to set a wide guard band when a range of components outside the frequency band is wide.
However, the interferences among the radio communication systems vary according to arrangements of base stations and mobile terminal devices constituting the radio communication systems, etc., so that they do not necessarily occur always. For this reason, an excessively wide guard band will only lower the frequency utilization efficiency.
For this reason, there is a known method (random assignment by carrier sense) in which a noise component of a frequency desired to be used is measured in advance, a frequency with a large noise power is regarded as receiving interferences from other radio communication system, and a frequency with a small noise power is used.
Now, in the radio communication device, the spurious components such as higher harmonic components of the carrier component, the intermodulation distortion components, etc., are generated due to the non-linearity of the amplifier, etc. There are cases where these spurious components are generated in a frequency region largely separated from the carrier frequency such that they become components outside the frequency band that can be used by that system.
However, in the random assignment described above, whether or not the spurious components generated outside the frequency band of that system are going to cause interferences to the other radio communication systems when the specific frequency is used by that system has not been judged.